\begin{tikzpicture}[>=Stealth]
    \node[draw, align=left] at (0,2) {任意负角的 \\ 三角函数};
    \node at (2.3,2.4) {用公式三、一};
    \draw[->] (1.2,2) -- (3.7,2);

    \node[draw, align=left] at (4.8,2) {任意正角的 \\ 三角函数};
    \node at (6.8,2.4) {用公式一};
    \draw[->] (6,2) -- (7.8,2);

    \node[draw, align=left] at (0.2,0) {$0^\circ$ \~{} $360^\circ$ 间角 \\ 的三角函数};
    \node at (2.8,0.4) {用公式};
    \draw[->] (1.7,0) -- (3.9,0);
    \node at (2.8,-0.4) {二、四、五};

    \node[draw, align=left] at (5.2,0) {$0^\circ$ \~{} $90^\circ$ 间角 \\ 的三角函数};
    \node at (7.0,0.4) {查表};
    \draw[->] (6.6,0) -- (7.5,0);

    \node[draw, align=left] at (8,0) {求 \\ 值};
\end{tikzpicture}
